1. Field of the Invention
This invention relates generally to cutters for machine tools, and more particularly to a countersink cutter.
2. Description of the Prior Art
Many machined products require that drilled holes be countersunk. Originally this required that the hole first be drilled with a drill and then countersunk with a countersink. Then it was discovered that a countersink could be combined with a drill. Such an arrangement is very common in "center drills", where the countersink and drill are combined in one piece of tool steel, and used to drill and countersink the ends of a shaft for mounting on center in a lathe or the like.
One of the most recent developments of which I am aware in the combination of a drill with a countersink, is represented by a product of the Severance company of Saginaw, Mich. It is a countersink. Instead of a shank at the end opposite the cutting teeth, for mounting in a chuck, it has a central aperture extending from the rear end toward the cutting teeth. This aperture is of a diameter sufficient to receive a twist drill through the center of it, with the drill axis colinear with the rotational axis of the countersink cutting teeth. The teeth project slightly into the valleys (gullets) of the flutes. Therefore, although the central aperture is large enough for the drill shank to be received through it, the countersink is mounted onto the drill at the drill point so that the innermost tips of the countersink teeth can be received in the valleys of the flutes. The countersink has diametrically opposed transverse threaded apertures in the side of it intercepting the central aperture so that a set screw received in each of the apertures can be received in the flutes and tightened on opposite sides of the drill web, to hold the countersink in place. This has a disadvantage in that it requires that the set screws be carefully located on the drill. It is difficult to avoid a tendency of the countersink to work upward on the drill, during use.
The other drill-mounted countersink of which I am aware is one sold by Vernon Devices, Inc. of Mount Vernon, N.Y. It has a countersink mounted on the drill much like the above described countersink. The one cutting tooth does not project into the drill flute. In addition to a set screw holding the countersink directly to the drill, this device uses a separate collar fastened to the drill by a set screw. This collar is mounted end-to-end with the countersink. The collar has an axially extending threaded portion receiving a set screw in it. The axially extending set screw is screwed into the collar until it projects against the rear end of the countersink. It is further screwed into the collar and, bearing on the countersink, tends to put a slight misalignment of the countersink portion with the collar portion and thereby tighten these portions on the drill to keep them from moving rotationally or longitudinally. This has a disadvantage in that it puts a bending force on the drill, with the attendant irregularity of hole size or shape, and stress on the drill.